前言
golang是一门极具设计哲学的语言，其中一点是没有支持包循环导入，目的是迫使 Go 程序员更多地考虑程序的依赖关系。一方面保持依赖关系图的简洁，二是快速的程序构建。
通常来说，只要你的包规划得好，严格规范单向调用链（如控制层->业务层->数据层），一般不会出现包循环引用问题。当然现实业务往往不会这么理想，同层级之间的不同包经常需要互相引用，下面我就分享几种解决包循环引用的方案。
抽象接口
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package package_i
type PackageAInterface interface {
PrintA()
}
type PackageBInterface interface {
PrintB()
}
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package package_a
import (
"cycle/package_i"
"fmt"
)
type PackageA struct {
B package_i.PackageBInterface
}
func (a PackageA) PrintA() {
fmt.Println("I'm a!")
}
func (a PackageA) PrintAll() {
a.PrintA()
a.B.PrintB()
}
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package package_b
import (
"cycle/package_i"
"fmt"
)
type PackageB struct {
A package_i.PackageAInterface
}
func (b PackageB) PrintB() {
fmt.Println("I'm b!")
}
func (b PackageB) PrintAll() {
b.PrintB()
b.A.PrintA()
}
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package main
import (
"cycle/package_a"
"cycle/package_b"
)
func main() {
a := new(package_a.PackageA)
b := new(package_b.PackageB)
a.B = b
b.A = a
a.PrintAll()
b.PrintAll()
}
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三、新建公共组合包（子包），在组合包中组合调用
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package package_c
import (
"cycle/package_a"
"cycle/package_b"
)
type CombileAB struct {
A *package_a.PackageA
B *package_b.PackageB
}
func (c CombileAB) PrintAll() {
c.A.PrintA()
c.B.PrintB()
}
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package main
import (
"cycle/package_a"
"cycle/package_b"
"cycle/package_c"
)
func main() {
a := new(package_a.PackageA)
b := new(package_b.PackageB)
c := new(package_c.CombileAB)
c.A = a
c.B = b
c.PrintAll()
}
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四、全局存储需要相互依赖的函数，通过关键字进行调用
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package callback_mgr
import (
"fmt"
"reflect"
)
var callBackMap map[string]interface{}
func init() {
callBackMap = make(map[string]interface{})
}
func RegisterCallBack(key string, callBack interface{}) {
callBackMap[key] = callBack
}
func CallBackFunc(key string, args ...interface{}) []interface{} {
if callBack, ok := callBackMap[key]; ok {
in := make([]reflect.Value, len(args))
for i, arg := range args {
in[i] = reflect.ValueOf(arg)
}
outList := reflect.ValueOf(callBack).Call(in)
result := make([]interface{}, len(outList))
for i, out := range outList {
result[i] = out.Interface()
}
return result
} else {
panic(fmt.Errorf("callBack(%s) not found", key))
}
}
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package package_a
import (
"cycle/callback_mgr"
"fmt"
)
func init() {
callback_mgr.RegisterCallBack("getA", new(PackageA).GetA)
}
type PackageA struct {
}
func (a PackageA) GetA() string {
return "I'm a!"
}
func (a PackageA) PrintAll() {
fmt.Println(a.GetA())
fmt.Println(callback_mgr.CallBackFunc("getB")[0].(string))
}
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package package_b
import (
"cycle/callback_mgr"
"fmt"
)
func init() {
callback_mgr.RegisterCallBack("getB", new(PackageB).GetB)
}
type PackageB struct {
}
func (b PackageB) GetB() string {
return "I'm b!"
}
func (b PackageB) PrintAll() {
fmt.Println(b.GetB())
fmt.Println(callback_mgr.CallBackFunc("getA")[0].(string))
}
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package main
import (
"cycle/package_a"
"cycle/package_b"
)
func main() {
a := new(package_a.PackageA)
b := new(package_b.PackageB)
a.PrintAll()
b.PrintAll()
}
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异步调用解耦
对于不需要执行结果的方法调用，可以采用事件总线进行异步调用。
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package eventBus
import (
"github.com/asaskevich/EventBus"
)
var globalEventBus EventBus.Bus
func init() {
globalEventBus = EventBus.New()
}
func Subscribe(topic string, fn interface{}) error {
return globalEventBus.Subscribe(topic, fn)
}
func SubscribeAsync(topic string, fn interface{}, transactional bool) error {
return globalEventBus.SubscribeAsync(topic, fn, transactional)
}
func Publish(topic string, args ...interface{}) {
globalEventBus.Publish(topic, args...)
}
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package package_a
import (
"cycle/eventBus"
"fmt"
)
func init() {
eventBus.Subscribe("PrintA", new(PackageA).PrintA)
}
type PackageA struct {
}
func (a PackageA) PrintA() {
fmt.Println("I'm a!")
}
func (a PackageA) PrintAll() {
a.PrintA()
eventBus.Publish("PrintB")
}
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package package_b
import (
"cycle/eventBus"
"fmt"
)
func init() {
eventBus.Subscribe("PrintB", new(PackageB).PrintB)
}
type PackageB struct {
}
func (b PackageB) PrintB() {
fmt.Println("I'm b!")
}
func (b PackageB) PrintAll() {
b.PrintB()
eventBus.Publish("PrintA")
}
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